In the theoretical assumption of informational cascades, private signals and predecessors' actions are equivalently informative before informational cascades, but are not once informational cascades have started. This experimental study tests this assumption by measuring the informativeness of private signals and predecessors'' actions for human subjects in and out of informational cascades. We observed that subjects in informational cascades do not extract much information from predecessors'' actions, indicating that they recognize other subjects'' cascading behaviors, that subjects rely more on their private signals than on predecessors'' actions even when both of them are equivalently informative, and that subjects cannot estimate posterior beliefs precisely in a Bayesian way due to cognitive biases such as anchoring and adjustment or conservatism.